Electric reduction of refractory metallic compounds



(No Model.)

T. L. WILLSON. ELECTRIC REDUCTION OB RBFRACTORY METALLIC COMPOUNDS.

Patented Feb. 21, 1893.

UNITED STATES PATENT OFFICE.

THOMAS I. WILLSON, or LEAKsvlLLE, NORTH caserma' ELECTRIC REDUCTION 0F REFRACTORY METALLIC CUMIZOUNDS.'

sPEcmcA'rroN forming part of were Patent No. 492.877, dama February a1, 189s.

` pulman mea ma 9,1m. sam nu. meer. m0 mm To all whom it may concern:

Be it known that I, THQHAS L. VILLSOrLa citizen of the United States, residing at Leaksville, in the county of Rockingham and State 'of North Carolina, have invented certain new and useful Improvements in the Electric Reduction of Refractory Metallic Compounds, of which the following is aspecitication.

This invention relates to the reduction of aluminium and otherditiicultly reducible metals from refractory ores or componndsthereof by mcansof electric smelting. Electric 'smelting, or metallurgical reduction by means of elecfricallygeneratedheat,hasheretoforebeen performcdintwoways,uamely,byanincandescent fn rnaee heated by the passage of an electric current. through a mass of broken carbon, the heat being generated by the resistance which this poor conductor presents to the passage of the electric current; and in au arc furnace wherein the heat is generated by the passage of an electric current across an arc between two separated electrodes. In the former or incandescent furnace, the current is passed horizontally between two carbon bars or electrodes, the space between them being lilled with a mixture of broken carbon and the ore to be reduced, and with a base metal, as copper. Such furnaces are subject to the practical disadvantage that as the base metal fuses a pool or bath is formed extending between the Aelectrodes and serving to short-circuit them around the mass of material to be reduced, which necessitates the continual drawing apart of the electrodes in order to maintain the necessary resistance in the furnace. This difficulty is in great measure overcome by the use of an arc furnace in which the current passes vertically between two electrodes, one of which consists of a carbon or graphite crncible or hearth, and the other a carbon bar or pencil above and entering the hollow of the crncible or hearth. The pencil being lowered into contact with the crncible or an intervening conducting material, is raised out of con tact therewith to produce an arc, the heat of which performs the reduction of the material` placed in the crncible. As reduction in an are furnace has been practiced priorto my invention, the alumina or other refractory ore is fused by the heat of the arc and covers the bottom of the crncible in a molten poo1`ol fbath. In the direct manufacture of bronzes or other alloys the hase metal thereof forms a pool at the bottom of the crncible, and the molten alumina or otherore lies in a bath snperposed thereupon. The carbon pencil is kept elevated above the surface of the bath of alumina in order to maintain the arc. A reducing agent being present in the furnace, either by introducing a reducing atmosphere therein, or by the utilization of the carbon of the electrodes as such agent, the reduction of the alumina or other metallic compound is effected by the combined action of the electric arc and the reducing agent. When a base metal is present it combines with the reduced metal, forming an alloy.

In the operation of such an electric arc furnace, considerable practical ditlicnlty is experienced by reason of the sudden and violent tlnctnations in the resistance of the furnace, which occur by reason of the ebullition of the fused bath. The fused alumina or other ore or metallic compound, beinga much better electrical conductor than the vaporous medium of the arc, must be kept out of contact with the carbon pencil in orderto maintain an arc. By the ebullition of this fused bath, the liquid aluminaor other ore is caused tospatter, or spout, or foam, upwardly at frequent irregular intervals, into contact with the carbon pencil, thereby to a great extent short-circniting the arc and lowering the resistance -of the furnace., In practice, it is found that this boiling up of the alumina produces 'a shortfcircnit of such very low re' shock, these shocks following each other in such rapid and irregular succession as to be which the power is transmitted, to a severe,

elitremely injurious and detrimental to the machinery, 'lhere is furthermore great liability of burnmg cnt the armature of the dyllt `tramo by reason of the excessivecurrent, even 1in the case of dynamos whose armatures are constructed to carry currents of extraordinary volume such as must be used for electro-metallurgical work. This short-circuiting bf the are is perhaps partly due to the boil'- ing up of' the copper or othcr'base metal through the bath of alumina. or other orc when, as in the making of aluminium bronze, such a base metal is present in the furnace; but the same diiiieulty is experienced, and to nearly or quite the same degree, when no base metal is present in the furnace, and when consequently the only fluid bath is that `of the alumina or otherfore under treatment.

The object of my present invention is to overcome the practical diiiicultes arising from the presence in the furnace of a fused bath of the ore or compound under treatment. Iu the course of numerous experiments that l have made, and the use of various reducing agents, I have discovered that subdivided or pulverized carbon when com mingled withthe alumina or other metallic compound to be reduced, and in sufficient proportions, has the effect Aof preventing the formation of a bath of the fused metallic compound.

My present invention therefore consists as an improvement in electric smelting in an arc or vertical furnace in subjecting alumina or other refractory metallic compound to the continued heat of an electric arc while commingled with subdivided carbon in sufficient proportion to prevent the formation of a bath of the fused compound. The violent fluctuations in the resistance 'of the arc due to the `ebullition of such a bath are consequent-ly avoided, and the resistanceof the arc is rendered'so nearly uniform asto render the smelting process of practical operation in connection with existing means for generating the requisite heavy electrical currents. Such' :fluctuations as occur are so tri fling in extent, and so gradual, that the machinery is subjected to novinjurious strains. The smelting process is also rendered more economical because it is conducted more regularly and progressively, is subject to less interruption by reason of the slowing down of the dynamo, such as results from the occurrence of a seripus shortcircuit, and is consequently effected by the maximum current that the ydynamo can generate under the requisite resistance `of the furnace.

In the practice of my present`invention I employ by preference an electric furnace of the construction and proportions shown in the accompanying drawing, which shows the `furnace in vertical mid-section, the electric circuit and the dynamo Ibeing shown diagrammatically.

Referring to the the outer masonry shell orbench ofthe fur nace, B the carbon or graphite crucible,'or hearth, C the carbon bar or pencil constituting the movable eleotrode,andD the dynamo `for generating the currents. Iliroxnthe tcrmhV drawings, let A designate nal brushes of this dynamo, one wire w leads to and communicates with the crucible B, while the other .wire w' leads to and communicates with the carbon. pencil C. The connections are preferably made in the manner shown, the wire w being connected through a fastening bar a to au iron plate b underlying the crucible l, and the wire w' being connected to a metal socket c embracing the upper end of the carbon pencil C. The bench A is made preferably of tirebrick, which is a non-conductor of electricity, and the furnace is covered over with a plate, or preferably two plates E E of carbon, having a central hole through which the carbon pencil C projects down into the crucible.

For tapping out the resulting product, a tap-hole d is formed which in operation is closed by a ping e of alumina, clay, or other suitable refractory material. The carbon plates E E rest on the top of the liirebrick walls A, whichl project above the top of the crucible, forming an intervening space f for insulatingr purposes to prevent the short-circuiting of the furnace between B and E.

For the vertical adjustment of the' carbon pencil, a screw-threaded shaft g is provided which may be propelled up and down by the engagement therewith of a suitably mounted rotative nut h. The details shown, however, are not essential to my invention, which may be applied in connection with furnaces widely different from that shown. The dynamo being in operation and the electrical connections properly made, the 'carbon pencil C is thrust down until its end touches the bottom or hearth of the crucible, thereby closing the circuit. The pencil is thereupon slightly elevated in order to cause an are to spring between the crucibl'e and the pencil. This are is preferably permitted to play for a minute or more before putting any material into the furnace, in order to first thoroughly heat up the furnace. Thereupon some alumina or other refractory metallic compound, prefer# ably thoroughly commiugled or intermixed with finely divided carbon, is introduced'into the furnace, which may e done by shoveling the charge through a top opening 'i formed as a notch -in the brickyvork A. The granular material thus introduced falls around the lower end of the carbon pencil, and if it comesin contact therewith, and is itself suf- IIO ticiently conductive, it may extiu uish the arc, in which case the attendant wi l lift the carbon pencil somewhat higher in order to re-establish the are.' The reduction then 'proceeds, either gradually or Iviolently by a sa ries of explosions according to the nature of the materials introduced. Nor fused bath is within the erucible. The presence of the subdivided carbonl appears to have dthe effect of maintaining the subdivision of the alumina asthe latter becomesfused, and perhapsto son e extent-.of absorbin it, the alumina boing thus 'held by the car n untilthe intense formed, and consequently no ebullition occurs' while the reduction is at its Height, and

`the immediate cooling down of 'the furnace, A no cake of solidified alumina'is found such aswould result from the presence of a molten I -bathbut on the contrary the materialin thef is found in apparently the same condition as before its introduction into the fur- 1 nace, beingapowdered or granulated alumina Y intermixed or impregnated with carbon, and

ordinarily noteven agglomerated by the heat, ln the reduction of aluminium by this method, the aluminiumfreed within the furnace must be recovered in some way before it can esespe into ccntact with the air and be oxidized.

The particular means for recovering the aluminium terms no essential part o f my pres eut invention, but there are two methods .which as l believe may be used for this pur- O these, they rst is to introduce a base metalI in to the furnace to instantly alloy with the nascent aluminium as it is freed, this g the method commonly heretofore emplayed. The second methd is to have an excess of carbon in the crucible sncient to combine with the nascent aluminium, forming an aluminium carbide, from which the metal may be subsequently extracted. The result of suppressing the fused bath and consequent ebullition will not be attained unless the carbon commingled with the ore or compound under treatment be in suiicent proportion. The proportion required will vary according to the condition of the ore and carbon, varying with their tineness and the de-` of intimacy of theiradmixtura. When alumina is used in the form of a line powder, and the carbon is combined with it with the utmost intimacy by impregnating the alumina witlrthe carbon, l have found that an amount of carbon equal by weight to dfteen per cent. of Zthe mixture, is sucient to prevent the formation of a fused bath. If the material is in coarser form, and less intimately ecmmingled, a largerpercentageof carbon may he' required. l prefer to use alumiuaor other ore or compound impregnated with coal tar or etherhvy suitable hyd ro-carbon, by stirring powdered or granulated aluminanor other metallic compound into the tar or other hydrocarbon while the latter is maintained in the liquid state, preferably by being heated, until the alumina &c. is thoroughly impregnated with the hydro-carbon, and thereupon driving olf` the hydrogenY and lighterhydro-carbons by heat until the whole is reduced to a drypowder. This tar-impregnated alumina i is` claimed in my applition for patent led April 20, 1892, Serial No. 429,923. In lieu however, eomminnted alumina. er

metallic-compound to be reducefLaid wdeer com carbonimayhe meij vided carbon with 'the material tobe reduced 7:.

is not essential to 'my present invention, it being only essential thereto that while the material under treatment is being subjected to the continued heat of theelectrc arc, sub; divided carbon in suicent be commingled with it. Thus the actual iutermixture of the two may first take place in the arc itself. Y

I have found that by iirst introducing alu- `mina and fusingit in the furnace so that it is brought into the condition of a molten bath, and when it reaches such a state of ebullition as to cause serious fluctuations iu the resistance of the furnace, the introduction into the crucible of the requisite proportion of com minuted or subdivided carbonwill quickly suppress the ebullition and bring the resistance of the furnace tosubstantial uniformity. In this case the carbon is commingled with the aluminaby'rcasou of the violent circulation of the latter due to its ebullition, the suppression of the ebullition occurring apparently'immediately upon the thorough commingling of' the introduced carbon with the alumina.

In practicing my process for the production of aluminium bronze, I find it preferable after initially heating up the furnace,to first introduce the copper, which instantly fuses and forms a pool of molten base metal in the bottom of the crucible,and thereafter to introduce the tar-impregnated alumina, or intermixed alumina and powdered carbon as the case may be, lifting the carbon pencil sutilcient-ly to maintain the arc. The copper, and the alumina and carbomare preferably introduced in small quantities or charges and at frequent intervals, and preferably in alternation. As the reduction proceeds,the pool of copper at the bottom of the crucible is converted into aluminium-bronze, the quantity of which gradually increases, until after a run of several hours it is tapped out of the crucible without cooling down the furnace, whereupouthecarbon pencilis readjustedand the ope eration proceeded with with only momentary interruption. The pool or bath of molten alumiuium bronze is not subject to anymaterial degree of ebullition, since it is heated only from above, so that what vaporization occurs is only at its upper surface, and consequently nolbnbbles of vapor rise up through it. A The current passing through it generates practically no heat, since the molten metal is in excellent conductor. It is only in the case of a superposed bath of molten ore that dihiclty proportion shall 'r oo IIO is experienced in the short-circuiting ofthe "arc, since this ore being a somewhat poor con-f dnctor,is heated by the passpge of the current through it, as well as by the heat of the are immediately above it, and is kept in violent Y-ehullition. But byY my invention the keluliliticu1- of the molten ores wholly prerent upwardly through the furnace, or the reverse arrangement may be made, thereby passing the current downwardly through the furnace. I prefer the upward passage of the current because I find that it involves much less wasting away of the electrodes' B C by oxidation. The crucible B is so thoroughly' protected by the presence of the material being acted upon,.that itis but slightly oxidized in any event, and by making the carbon pencil C the negative electrode, it is caused to waste away much less rapidly than if it were made the positive. Furthermore, the presence of l the inter-commingled carbon which serves as a reducing agent almost wholly pre'- vents the oxidation of the electrodes, since the oxygen which is dissociated from the alumina is instantly taken up by the intercommingled carbon, which is in closer proximity to the points of evolution of the oxygen than are the surfaces of the electrodes, and consequently the oxygen is almost wholly reduced to carbon monoxideor dioxide before it. comes in contact with the electrodes..

My'present invention is not applicable to incandescent furnaces, that is to say, those in which the heat is generated by passingacur rent through a broken resistance material,

, such as retort carbon, and I -specifically disclaim its application to such furnaces. My invention is applicable only where the heat is derived from the electricv arc. The conditions essential to the maintenance of such an arc in an electric furnace are well understood in the art. The arc is caused by the separation of the electrodes, thereby forming an interruption in the circuit, and to maintain the arc, at least one of the electrodes must be maintained out of contact-with any conducting material in thev furnace ofy such low resistance as to shunt sucient current around the arc to extinguish the arc. 4In any case the arc is formed and maintained close over the material under treatment, or at least close over such portion of the material as is immediately under treatment.

. The best arrangement for producing an arc is that shown, wherein the current passes in vertical direction througha furnace, the crucible constitutingone electrode, and a carbon pencil thrust into it constituting the other. Other arrangements, however, are admissible, although believed to be inferior. For example,two carbon pencils may be connected to the respective terminals of the circuit and thrust 5 into a 'crucible or arranged close over a hearth -yzlhich might be non-conducting), being separated to forin an' arc between them, which arc is broughtV downvinto close contact-with the material under treatment, or, they may be so strontium, magnesium, titanium, tungsten,

and zirconium. In the manufacture of bronzes, I propose to apply it to the manufacture of bronzes containing silicon and boron.

My invention is applicable to other chemical reactions than those included by the word reduction used merely iu its metallurgical sense; forexample, I propose to apply it for the treatment of refractory compounds or ores of metals, not necessarily for the production of the metals themselves, but for the production of other compounds thereof. For example, Ihave already employed it for reducing calcium oxide and producingcalcinm carbide.

Iclaim as my invention'the .following defined novel features, substantiallyas hereinbefore specified, namely:

1. The process of decomposing refractory compounds which consists in subjecting the compound, while commingled. with subdivided carbon in suicient, proportion to prevent the formation of a bath of fused compound, to the continued heat of an electric arcbetween separated electrodes, one (at least) of which is arranged close above the material immediately under treatment, so that the arc is close above such' material, whereby during the operation the fluctuations in the resistance of the arc which would be due to the presence and ebullition of such -bath are avoided.

2. The process of deoxidizing refractory metallic compounds which consists in subjecting the compound,while commingled with subdivided carbon in' suflcient proportion to prevent the formation of a bath of fused com-V sistance of the arc which would bev due to the presence and ebnllition of such bath are avoided.

3. The process of reducing refractory metallic compounds which consists in subjecting Vthe compound, while commingled with subdivided carbon in sufficient proportion to prevent the formation of a bath of fused compound, to the continued heat 'of an electric arc produced by passing a current in approximately vertical direction between separated electrodes, so that the arc is maintained close above the material immediately7 under treatment whereby during,r the reduction the fluctuations in the resistance of the arc which v would bedue to the presence and ebullition of such bath are avoided.

IIO

A -fThe process of reducing alumina which consists-in subjecting it, While commingled with subdivided carbon in suiicient proportion to prevent-the formationV of a bath of fused alumina, tothe continued heat-of an electric arc between ,separated electrodes one above the other, so that the arc is maintained close above the material immediately under treatment whereby during the reduction the uctnations in the resistance .of the-arc which would be due to the presence of such bath are avoided. i

`5. The process of reducing a refractory mef tallio compound which consists in commingiing therewith asuicient proportion of finely subdivided carbon as described,d feeding the I mixture into an electric arc,Y maintained 'be-5 tween vertice-,ily separated electrodes, and maintaining it subject to the continued heat of such arc, and so that the arc is maintained zo presence of two subscribing 2.5 i 

